Effect Of Different Land Use Types On Storage And Structure Of Soil Organic Carbon In Stipa Klemenaii Steppe In Inner Mongolia

Grassland ecosystem to global climate change and has a great influence to the greenhouse effect, due to the unreasonable utilization, the natural grassland degradation is serious. Soil organic carbon (SOC) is important to grassland ecosystem carbon and nutrient elements, has been the focus in the study of ecology and soil science and one of the focus. In order to study the influence of SOC and its structural characteristics under different land use types, the combined methods of field sampling and laboratory analysis were employed to analyze the SOC storage in soil depth of 0～100 cm, the components of soil active organic carbon and 13C NMR spectroscopy was utilized to explor the structure of SOC in soil depth of 0-20 cm in Stipa klemenaii desert steppe in Inner Mongolia. The treatments included three grazing measures [0.50 sheep/hm2 (G0.50),0.94 sheep/hm2 (G0.94),1.25 sheep/hm2 (G1.25)], one fencing enclosure measure and one cultivating measure. Fencing enclosed area without livestock and human disturbance. Cultivating area planted corn (Zea mays) in accordance with the local general management. The results showed that:1. The effect of enclosure, grazing, and cultivating on soil physical and chemical and enzymatic activity of Stipa klemenaii desert grassland is different. Reclamation and grazing compared with enclosure, the content of soil total nitrogen and total phosphorus, and soil urease, catalase, alkaline phosphatase activity in different levels were reduced, and the soil pH value increased. With the increase of grazing intensity, the content of soil total nitrogen and total phosphorus, soil urease, alkaline phosphatase, catalase activity gradually reduce, soil pH value increased. Soil physical and chemical and urease activity along with the deepening of soil was reduced after the first rise trend, and reached the maximum in 30～40 cm. Alkaline phosphatase, catalase activity as the soil layer deepen gradually reduced.2. Compared with grazing and cultivating, the content, density and storage of SOC increased in the soil layers within 0～100 cm depth after four years enclosed. SOC content and SOC density increased first, and then decreased with the increase of soil depth. The highest value of SOC content and SOC density occurred at 20～30 cm or 30～40 cm soil layer.3. Grazing and cultivating significantly decreased the contents of DOC, ROC and MBC respectively compared to fencing enclosure. The contents of SOC and soil active organic carbon decreased gradually with increased in stocking rates. In general, the allocation proportion of active organic carbon increased in 0-20 cm soil layers after 4 years of fencing enclosure in Stipa klemenaii steppe, whereas which decreased after grazing and cultivating. The MBC/SOC of fencing enclosure was significantly higher than razing and cultivating. The contents of SOC, DOC, ROC and MBC were significantly positively related to relationship between each other. Soil active organic carbon and soil physical and chemical propertie have close relationship. These results indicated that fencing enclosure enhanced soil quality and improved the Stipa klemenaii steppe ecological environment.4. The SOC contained more alcoxyl and alkyl carbon than other carbon fractions. The average proportion of SOC fractions occurred as the order of alcoxyl carbon (34.86%～37.85%)> alkyl carbon (26.05%～33.87%)> aromatic carbon (0.60%-17.69%)> carbonyl carbon (14.57%-16.90%). The highest value of alkyl carbon and carbonyl carbon occurred at cultivating area, while the highest value of alcoxyl carbon and aromatic carbon occurred at G1.25. The ratio of alkyl-C/O-alkyl-C performance for G1.25> G0.94> cultivating area> G0.50> enclosed. Aromaticity performance for G1.25> G0.94> cultivating area> G0.50> enclosed. Enclosed makes the SOC structure tend to become more alkyl, and thus is beneficial for maintaining soil fertility.